Chunk up decryption

Split up large segments that need AES-128 decryption and hand control back to the browser between segments. Clean up the decryption block loop a bit since it's no longer critical to finish before the next frame is rendered.

@@ -38,7 +38,18 @@
 (function(window, videojs, unpad) {
 'use strict';
 
-var AES, decrypt;
+var AES, AsyncStream, Decrypter, decrypt, ntoh;
+
+/**
+ * Convert network-order (big-endian) bytes into their little-endian
+ * representation.
+ */
+ntoh = function(word) {
+  return (word << 24) |
+    ((word & 0xff00) << 8) |
+    ((word & 0xff0000) >> 8) |
+    (word >>> 24);
+};
 
 /**
  * Schedule out an AES key for both encryption and decryption. This
@@ -221,7 +232,7 @@ AES.prototype = {
 decrypt = function(encrypted, key, initVector) {
   var
     // word-level access to the encrypted bytes
-    encrypted32 = new Int32Array(encrypted.buffer),
+    encrypted32 = new Int32Array(encrypted.buffer, encrypted.byteOffset, encrypted.byteLength >> 2),
 
     decipher = new AES(Array.prototype.slice.call(key)),
 
@@ -233,7 +244,6 @@ decrypt = function(encrypted, key, initVector) {
     // decrypted data
     init0, init1, init2, init3,
     encrypted0, encrypted1, encrypted2, encrypted3,
-    decrypted0, decrypted1, decrypted2, decrypted3,
 
     // iteration variable
     wordIx;
@@ -250,49 +260,25 @@ decrypt = function(encrypted, key, initVector) {
   for (wordIx = 0; wordIx < encrypted32.length; wordIx += 4) {
     // convert big-endian (network order) words into little-endian
     // (javascript order)
-    encrypted0 = (encrypted32[wordIx] << 24) |
-      ((encrypted32[wordIx] & 0xff00) << 8) |
-      ((encrypted32[wordIx] & 0xff0000) >> 8) |
-      (encrypted32[wordIx] >>> 24);
-    encrypted1 = (encrypted32[wordIx + 1] << 24) |
-      ((encrypted32[wordIx + 1] & 0xff00) << 8) |
-      ((encrypted32[wordIx + 1] & 0xff0000) >> 8) |
-      (encrypted32[wordIx + 1] >>> 24);
-    encrypted2 = (encrypted32[wordIx + 2] << 24) |
-      ((encrypted32[wordIx + 2] & 0xff00) << 8) |
-      ((encrypted32[wordIx + 2] & 0xff0000) >> 8) |
-      (encrypted32[wordIx + 2] >>> 24);
-    encrypted3 = (encrypted32[wordIx + 3] << 24) |
-      ((encrypted32[wordIx + 3] & 0xff00) << 8) |
-      ((encrypted32[wordIx + 3] & 0xff0000) >> 8) |
-      (encrypted32[wordIx + 3] >>> 24);
+    encrypted0 = ntoh(encrypted32[wordIx]);
+    encrypted1 = ntoh(encrypted32[wordIx + 1]);
+    encrypted2 = ntoh(encrypted32[wordIx + 2]);
+    encrypted3 = ntoh(encrypted32[wordIx + 3]);
 
     // decrypt the block
-    decipher.decrypt(encrypted0, encrypted1, encrypted2, encrypted3, decrypted32, wordIx);
+    decipher.decrypt(encrypted0,
+                     encrypted1,
+                     encrypted2,
+                     encrypted3,
+                     decrypted32,
+                     wordIx);
 
     // XOR with the IV, and restore network byte-order to obtain the
     // plaintext
-    decrypted0 = decrypted32[wordIx]     ^ init0;
-    decrypted1 = decrypted32[wordIx + 1] ^ init1;
-    decrypted2 = decrypted32[wordIx + 2] ^ init2;
-    decrypted3 = decrypted32[wordIx + 3] ^ init3;
-
-    decrypted32[wordIx] = decrypted0 << 24 |
-      ((decrypted0 & 0xff00) << 8) |
-      ((decrypted0 & 0xff0000) >> 8) |
-      (decrypted0 >>> 24);
-    decrypted32[wordIx + 1] = decrypted1 << 24 |
-      ((decrypted1 & 0xff00) << 8) |
-      ((decrypted1 & 0xff0000) >> 8) |
-      (decrypted1 >>> 24);
-    decrypted32[wordIx + 2] = decrypted2 << 24 |
-      ((decrypted2 & 0xff00) << 8) |
-      ((decrypted2 & 0xff0000) >> 8) |
-      (decrypted2 >>> 24);
-    decrypted32[wordIx + 3] = decrypted3 << 24 |
-      ((decrypted3 & 0xff00) << 8) |
-      ((decrypted3 & 0xff0000) >> 8) |
-      (decrypted3 >>> 24);
+    decrypted32[wordIx]     = ntoh(decrypted32[wordIx] ^ init0);
+    decrypted32[wordIx + 1] = ntoh(decrypted32[wordIx + 1] ^ init1);
+    decrypted32[wordIx + 2] = ntoh(decrypted32[wordIx + 2] ^ init2);
+    decrypted32[wordIx + 3] = ntoh(decrypted32[wordIx + 3] ^ init3);
 
     // setup the IV for the next round
     init0 = encrypted0;
@@ -301,11 +287,79 @@ decrypt = function(encrypted, key, initVector) {
     init3 = encrypted3;
   }
 
-  // remove any padding
-  return unpad(decrypted);
+  return decrypted;
+};
+
+AsyncStream = function() {
+  this.jobs = [];
+  this.delay = 1;
+  this.timeout_ = null;
+};
+AsyncStream.prototype = new videojs.Hls.Stream();
+AsyncStream.prototype.processJob_ = function() {
+  this.jobs.shift()();
+  if (this.jobs.length) {
+    this.timeout_ = setTimeout(videojs.bind(this, this.processJob_),
+                               this.delay);
+  } else {
+    this.timeout_ = null;
+  }
+};
+AsyncStream.prototype.push = function(job) {
+  this.jobs.push(job);
+  if (!this.timeout_) {
+    this.timeout_ = setTimeout(videojs.bind(this, this.processJob_),
+                               this.delay);
+  }
+};
+
+Decrypter = function(encrypted, key, initVector, done) {
+  var
+    step = Decrypter.STEP,
+    encrypted32 = new Int32Array(encrypted.buffer),
+    decrypted = new Uint8Array(encrypted.byteLength),
+    i = 0;
+  this.asyncStream_ = new AsyncStream();
+
+  // split up the encryption job and do the individual chunks asynchronously
+  this.asyncStream_.push(this.decryptChunk_(encrypted32.subarray(i, i + step),
+                                            key,
+                                            initVector,
+                                            decrypted,
+                                            i));
+  for (i = step; i < encrypted32.length; i += step) {
+    initVector = new Uint32Array([
+      ntoh(encrypted32[i - 4]),
+      ntoh(encrypted32[i - 3]),
+      ntoh(encrypted32[i - 2]),
+      ntoh(encrypted32[i - 1])
+    ]);
+    this.asyncStream_.push(this.decryptChunk_(encrypted32.subarray(i, i + step),
+                                              key,
+                                              initVector,
+                                              decrypted));
+  }
+  // invoke the done() callback when everything is finished
+  this.asyncStream_.push(function() {
+    // remove pkcs#7 padding from the decrypted bytes
+    done(null, unpad(decrypted));
+  });
+};
+Decrypter.prototype = new videojs.Hls.Stream();
+Decrypter.prototype.decryptChunk_ = function(encrypted, key, initVector, decrypted) {
+  return function() {
+    var bytes = decrypt(encrypted,
+                        key,
+                        initVector);
+    decrypted.set(bytes, encrypted.byteOffset);
+  };
 };
+// the maximum number of bytes to process at one time
+Decrypter.STEP = 4 * 8000;
 
 // exports
 videojs.Hls.decrypt = decrypt;
+videojs.Hls.Decrypter = Decrypter;
+videojs.Hls.AsyncStream = AsyncStream;
 
 })(window, window.videojs, window.pkcs7.unpad);

@@ -633,6 +633,8 @@ videojs.Hls.prototype.loadSegment = function(segmentUri, offset) {
     responseType: 'arraybuffer',
     withCredentials: settings.withCredentials
   }, function(error, url) {
+    var segmentInfo;
+
     // the segment request is no longer outstanding
     tech.segmentXhr_ = null;
 
@@ -665,12 +667,26 @@ videojs.Hls.prototype.loadSegment = function(segmentUri, offset) {
     // if the segment is the start of a timestamp discontinuity,
     // we have to wait until the sourcebuffer is empty before
     // aborting the source buffer processing
-    tech.segmentBuffer_.push({
+    segmentInfo = {
+      // the segment's mediaIndex at the time it was received
       mediaIndex: tech.mediaIndex,
+      // the segment's playlist
       playlist: tech.playlists.media(),
+      // optionally, a time offset to seek to within the segment
       offset: offset,
-      bytes: new Uint8Array(this.response)
-    });
+      // unencrypted bytes of the segment
+      bytes: null,
+      // when a key is defined for this segment, the encrypted bytes
+      encryptedBytes: null,
+      // optionally, the decrypter that is unencrypting the segment
+      decrypter: null
+    };
+    if (segmentInfo.playlist.segments[segmentInfo.mediaIndex].key) {
+      segmentInfo.encryptedBytes = new Uint8Array(this.response);
+    } else {
+      segmentInfo.bytes = new Uint8Array(this.response);
+    }
+    tech.segmentBuffer_.push(segmentInfo);
     player.trigger('progress');
     tech.drainBuffer();
 
@@ -685,12 +701,15 @@ videojs.Hls.prototype.loadSegment = function(segmentUri, offset) {
 videojs.Hls.prototype.drainBuffer = function(event) {
   var
     i = 0,
+    segmentInfo,
     mediaIndex,
     playlist,
     offset,
     tags,
     bytes,
     segment,
+    decrypter,
+    segIv,
 
     ptsTime,
     segmentOffset,
@@ -700,28 +719,45 @@ videojs.Hls.prototype.drainBuffer = function(event) {
     return;
   }
 
-  mediaIndex = segmentBuffer[0].mediaIndex;
-  playlist = segmentBuffer[0].playlist;
-  offset = segmentBuffer[0].offset;
-  bytes = segmentBuffer[0].bytes;
+  segmentInfo = segmentBuffer[0];
+
+  mediaIndex = segmentInfo.mediaIndex;
+  playlist = segmentInfo.playlist;
+  offset = segmentInfo.offset;
+  bytes = segmentInfo.bytes;
   segment = playlist.segments[mediaIndex];
 
-  if (segment.key) {
+  if (segment.key && !bytes) {
+
     // this is an encrypted segment
     // if the key download failed, we want to skip this segment
     // but if the key hasn't downloaded yet, we want to try again later
     if (keyFailed(segment.key)) {
       return segmentBuffer.shift();
     } else if (!segment.key.bytes) {
+
       // trigger a key request if one is not already in-flight
       return this.fetchKeys_();
+
+    } else if (segmentInfo.decrypter) {
+
+      // decryption is in progress, try again later
+      return;
+
     } else {
       // if the media sequence is greater than 2^32, the IV will be incorrect
       // assuming 10s segments, that would be about 1300 years
-      var segIv = segment.key.iv || new Uint32Array([0, 0, 0, mediaIndex + playlist.mediaSequence]);
-      bytes = videojs.Hls.decrypt(bytes,
-                                  segment.key.bytes,
-                                  segIv);
+      segIv = segment.key.iv || new Uint32Array([0, 0, 0, mediaIndex + playlist.mediaSequence]);
+
+      // create a decrypter to incrementally decrypt the segment
+      decrypter = new videojs.Hls.Decrypter(segmentInfo.encryptedBytes,
+                                            segment.key.bytes,
+                                            segIv,
+                                            function(err, bytes) {
+                                              segmentInfo.bytes = bytes;
+                                            });
+      segmentInfo.decrypter = decrypter;
+      return;
     }
   }
 

-(function(window, videojs, undefined) {
+(function(window, videojs, unpad, undefined) {
   'use strict';
   /*
     ======== A Handy Little QUnit Reference ========
@@ -46,7 +46,7 @@ test('decrypts a single AES-128 with PKCS7 block', function() {
       0x82, 0xa8, 0xf0, 0x67]);
 
   deepEqual('howdy folks',
-            stringFromBytes(videojs.Hls.decrypt(encrypted, key, initVector)),
+            stringFromBytes(unpad(videojs.Hls.decrypt(encrypted, key, initVector))),
             'decrypted with a byte array key');
 });
 
@@ -68,8 +68,100 @@ test('decrypts multiple AES-128 blocks with CBC', function() {
     ]);
 
   deepEqual('0123456789abcdef01234',
-            stringFromBytes(videojs.Hls.decrypt(encrypted, key, initVector)),
+            stringFromBytes(unpad(videojs.Hls.decrypt(encrypted, key, initVector))),
             'decrypted multiple blocks');
 });
 
-})(window, window.videojs);
+var clock;
+
+module('Incremental Processing', {
+  setup: function() {
+    clock = sinon.useFakeTimers();
+  },
+  teardown: function() {
+    clock.restore();
+  }
+});
+
+test('executes a callback after a timeout', function() {
+  var asyncStream = new videojs.Hls.AsyncStream(),
+      calls = '';
+  asyncStream.push(function() {
+    calls += 'a';
+  });
+
+  clock.tick(asyncStream.delay);
+  equal(calls, 'a', 'invoked the callback once');
+  clock.tick(asyncStream.delay);
+  equal(calls, 'a', 'only invoked the callback once');
+});
+
+test('executes callback in series', function() {
+  var asyncStream = new videojs.Hls.AsyncStream(),
+      calls = '';
+  asyncStream.push(function() {
+    calls += 'a';
+  });
+  asyncStream.push(function() {
+    calls += 'b';
+  });
+
+  clock.tick(asyncStream.delay);
+  equal(calls, 'a', 'invoked the first callback');
+  clock.tick(asyncStream.delay);
+  equal(calls, 'ab', 'invoked the second');
+});
+
+var decrypter;
+
+module('Incremental Decryption', {
+  setup: function() {
+    clock = sinon.useFakeTimers();
+  },
+  teardown: function() {
+    clock.restore();
+  }
+});
+
+test('asynchronously decrypts a 4-word block', function() {
+  var
+    key =  new Uint32Array([0, 0, 0, 0]),
+    initVector = key,
+    // the string "howdy folks" encrypted
+    encrypted = new Uint8Array([
+      0xce, 0x90, 0x97, 0xd0,
+      0x08, 0x46, 0x4d, 0x18,
+      0x4f, 0xae, 0x01, 0x1c,
+      0x82, 0xa8, 0xf0, 0x67]),
+    decrypted;
+
+  decrypter = new videojs.Hls.Decrypter(encrypted, key, initVector, function(error, result) {
+    decrypted = result;
+  });
+  ok(!decrypted, 'asynchronously decrypts');
+
+  clock.tick(decrypter.asyncStream_.delay * 2);
+
+  ok(decrypted, 'completed decryption');
+  deepEqual('howdy folks',
+            stringFromBytes(decrypted),
+            'decrypts and unpads the result');
+});
+
+test('breaks up input greater than the step value', function() {
+  var encrypted = new Int32Array(videojs.Hls.Decrypter.STEP + 4),
+      done = false,
+      decrypter = new videojs.Hls.Decrypter(encrypted,
+                                            new Uint32Array(4),
+                                            new Uint32Array(4),
+                                            function(error, result) {
+                                              done = true;
+                                            });
+  clock.tick(decrypter.asyncStream_.delay * 2);
+  ok(!done, 'not finished after two ticks');
+
+  clock.tick(decrypter.asyncStream_.delay);
+  ok(done, 'finished after the last chunk is decrypted');
+});
+
+})(window, window.videojs, window.pkcs7.unpad);

@@ -152,10 +152,8 @@ module('HLS', {
 
     oldNativeHlsSupport = videojs.Hls.supportsNativeHls;
 
-    oldDecrypt = videojs.Hls.decrypt;
-    videojs.Hls.decrypt = function() {
-      return new Uint8Array([0]);
-    };
+    oldDecrypt = videojs.Hls.Decrypter;
+    videojs.Hls.Decrypter = function() {};
 
     // fake XHRs
     xhr = sinon.useFakeXMLHttpRequest();
@@ -173,7 +171,7 @@ module('HLS', {
     videojs.MediaSource.open = oldMediaSourceOpen;
     videojs.Hls.SegmentParser = oldSegmentParser;
     videojs.Hls.supportsNativeHls = oldNativeHlsSupport;
-    videojs.Hls.decrypt = oldDecrypt;
+    videojs.Hls.Decrypter = oldDecrypt;
     videojs.SourceBuffer = oldSourceBuffer;
     window.setTimeout = oldSetTimeout;
     window.clearTimeout = oldClearTimeout;
@@ -1878,6 +1876,10 @@ test('a new key XHR is created when a the segment is received', function() {
                            '#EXT-X-ENDLIST\n');
   standardXHRResponse(requests.shift()); // segment 1
   standardXHRResponse(requests.shift()); // key 1
+  // "finish" decrypting segment 1
+  player.hls.segmentBuffer_[0].bytes = new Uint8Array(16);
+  player.hls.checkBuffer_();
+
   standardXHRResponse(requests.shift()); // segment 2
 
   strictEqual(requests.length, 1, 'a key XHR is created');
@@ -1983,6 +1985,9 @@ test('skip segments if key requests fail more than once', function() {
   // key for second segment
   requests[0].response = new Uint32Array([0,0,0,0]).buffer;
   requests.shift().respond(200, null, '');
+  // "finish" decryption
+  player.hls.segmentBuffer_[0].bytes = new Uint8Array(16);
+  player.hls.checkBuffer_();
 
   equal(bytes.length, 2, 'bytes from the second ts segment should be added');
   equal(bytes[1], 1, 'the bytes from the second segment are added and not the first');
@@ -2007,9 +2012,8 @@ test('the key is supplied to the decrypter in the correct format', function() {
                          'http://media.example.com/fileSequence52-B.ts\n');
 
 
-  videojs.Hls.decrypt = function(bytes, key) {
+  videojs.Hls.Decrypter = function(encrypted, key) {
     keys.push(key);
-    return new Uint8Array([0]);
   };
 
   standardXHRResponse(requests.shift()); // segment
@@ -2017,7 +2021,7 @@ test('the key is supplied to the decrypter in the correct format', function() {
   requests[0].respond(200, null, '');
   requests.shift(); // key
 
-  equal(keys.length, 1, 'only one call to decrypt was made');
+  equal(keys.length, 1, 'only one Decrypter was constructed');
   deepEqual(keys[0],
             new Uint32Array([0, 0x01000000, 0x02000000, 0x03000000]),
             'passed the specified segment key');
@@ -2042,9 +2046,8 @@ test('supplies the media sequence of current segment as the IV by default, if no
                          'http://media.example.com/fileSequence52-B.ts\n');
 
 
-  videojs.Hls.decrypt = function(bytes, key, iv) {
+  videojs.Hls.Decrypter = function(encrypted, key, iv) {
     ivs.push(iv);
-    return new Uint8Array([0]);
   };
 
   requests[0].response = new Uint32Array([0,0,0,0]).buffer;
@@ -2052,7 +2055,7 @@ test('supplies the media sequence of current segment as the IV by default, if no
   requests.shift();
   standardXHRResponse(requests.pop());
 
-  equal(ivs.length, 1, 'only one call to decrypt was made');
+  equal(ivs.length, 1, 'only one Decrypter was constructed');
   deepEqual(ivs[0],
         new Uint32Array([0, 0, 0, 5]),
         'the IV for the segment is the media sequence');